org.jgroups.protocols
Class PEER_LOCK

java.lang.Object
  org.jgroups.stack.Protocol
      org.jgroups.protocols.Locking
          org.jgroups.protocols.PEER_LOCK

public class PEER_LOCK
extends Locking

Implementation of a locking protocol which acquires locks by contacting all of the nodes of a cluster.

Unless a total order configuration is used (e.g. SEQUENCER based), lock requests for the same resource from different senders may be received in different order, so deadlocks can occur. Example:

 - Nodes A and B
 - A and B call lock(X) at the same time
 - A receives L(X,A) followed by L(X,B): locks X(A), queues L(X,B)
 - B receives L(X,B) followed by L(X,A): locks X(B), queues L(X,A)
 

To acquire a lock, we need lock grants from both A and B, but this will never happen here. To fix this, either add SEQUENCER to the configuration, so that all lock requests are received in the same global order at both A and B, or use Lock.tryLock(long,java.util.concurrent.TimeUnit) with retries if a lock cannot be acquired.

An alternative is also the CENTRAL_LOCK protocol.

Since:

2.12

Author:

Bela Ban

See Also:

Locking, CENTRAL_LOCK

Nested Class Summary

protected class

PEER_LOCK.PeerLock Lock implementation which grants a lock when all non faulty cluster members OK it.

Nested classes/interfaces inherited from class org.jgroups.protocols.Locking

Locking.ClientCondition, Locking.ClientLock, Locking.LockingHeader, Locking.Request, Locking.ServerCondition, Locking.ServerLock, Locking.Type

Field Summary

Fields inherited from class org.jgroups.protocols.Locking

bypass_bundling, client_locks, local_addr, lock_listeners, server_locks, view

Fields inherited from class org.jgroups.stack.Protocol

down_prot, ergonomics, id, log, name, stack, stats, up_prot

Constructor Summary

PEER_LOCK()

Method Summary

protected Locking.ClientLock	createLock(java.lang.String lock_name)
void	handleView(View view)
protected void	sendAwaitConditionRequest(java.lang.String lock_name, Owner owner)
protected void	sendDeleteAwaitConditionRequest(java.lang.String lock_name, Owner owner)
protected void	sendGrantLockRequest(java.lang.String lock_name, Owner owner, long timeout, boolean is_trylock)
protected void	sendReleaseLockRequest(java.lang.String lock_name, Owner owner)
protected void	sendSignalConditionRequest(java.lang.String lock_name, boolean all)

Methods inherited from class org.jgroups.protocols.Locking

addLockListener, down, getAddress, getBypassBundling, getLock, getLock, getLock, getOwner, getView, handleAwaitRequest, handleCreateAwaitingRequest, handleCreateLockRequest, handleDeleteAwaitingRequest, handleDeleteAwaitRequest, handleDeleteLockRequest, handleLockDeniedResponse, handleLockGrantedResponse, handleLockRequest, handleSignalRequest, handleSignalResponse, notifyAwaited, notifyAwaiting, notifyLockCreated, notifyLockDeleted, notifyLocked, notifyUnlocked, printLocks, removeClientLock, removeLockListener, sendLockResponse, sendRequest, sendSignalResponse, setBypassBundling, unlockAll, up

Methods inherited from class org.jgroups.stack.Protocol

destroy, dumpStats, enableStats, getConfigurableObjects, getDownProtocol, getDownServices, getId, getIdsAbove, getLevel, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getUpServices, getValue, init, isErgonomics, printStats, providedDownServices, providedUpServices, requiredDownServices, requiredUpServices, resetStatistics, resetStats, setDownProtocol, setErgonomics, setId, setLevel, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, start, statsEnabled, stop

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

PEER_LOCK

public PEER_LOCK()

Method Detail

sendGrantLockRequest

protected void sendGrantLockRequest(java.lang.String lock_name,
                                    Owner owner,
                                    long timeout,
                                    boolean is_trylock)

Specified by:

sendGrantLockRequest in class Locking

sendReleaseLockRequest

protected void sendReleaseLockRequest(java.lang.String lock_name,
                                      Owner owner)

Specified by:

sendReleaseLockRequest in class Locking

sendAwaitConditionRequest

protected void sendAwaitConditionRequest(java.lang.String lock_name,
                                         Owner owner)

Specified by:

sendAwaitConditionRequest in class Locking

sendSignalConditionRequest

protected void sendSignalConditionRequest(java.lang.String lock_name,
                                          boolean all)

Specified by:

sendSignalConditionRequest in class Locking

sendDeleteAwaitConditionRequest

protected void sendDeleteAwaitConditionRequest(java.lang.String lock_name,
                                               Owner owner)

Specified by:

sendDeleteAwaitConditionRequest in class Locking

handleView

public void handleView(View view)

Overrides:

handleView in class Locking

createLock

protected Locking.ClientLock createLock(java.lang.String lock_name)

Overrides:

createLock in class Locking